Re: [Xen-devel] PVH CPU hotplug design document

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Jan 23, 2017 at 11:24:19AM -0500, Boris Ostrovsky wrote:
> On 01/23/2017 10:58 AM, Jan Beulich wrote:
> >>>> On 23.01.17 at 16:49, <boris.ostrovsky@xxxxxxxxxx> wrote:
> >> On 01/23/2017 10:43 AM, Boris Ostrovsky wrote:
> >>>>> From Linux perspective one option could be to have domU with PV-style
> >>>>> vCPU on/offlining based on xenstore and switch to ACPI hotplug if/when
> >>>>> it becomes available. This, however, will need an indication from the
> >>>>> hypervisor. We could, for example, set ACPI_FADT_HW_REDUCED, as we
> >>>>> discussed earlier.
> >>>> I think we shouldn't overload that flag. Didn't we settle already on 
> >>>> using
> >>>> two CPUID flags (of for PV-style onlining/offlining, the other for ACPI
> >>>> hot(un)plug)? With that I think I could then be talked into accepting the
> >>>> existence of two different models (and kernels could pick which one(s)
> >>>> they would like to support).
> >>> I forgot about existence of ACPI_FADT_HW_REDUCED until this morning,
> >>> which is why I mentioned it now.
> >>>
> >>> We can go with CPUID flags although I am not sure why we'd need two. I'd
> >>> think that OS can be expected to always support PV-style so the flag
> >>> would indicate support for ACPI-based hotplug.
> >> In fact, it doesn't matter whether OS supports PV-style hotplug. It's
> >> that Xen will always set appropriate xenstore entry. It's up to the OS
> >> whether to watch it and act upon this.
> > That's a good point, perhaps just one CPUID flag will do then indeed.
> 
> Roger, are you going to include this in your patchset or do you want me
> to do it?

I think this should be introduced in your DomU ACPI CPU hotplug series, and not
set for Dom0 until we found a way to perform ACPI vCPU hotplug for Dom0 also.

Roger.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel